Liquation is the melting of stibnite into “crudum” or “needle antimony”. It is
carried out between 550 and 600 degrees C. If the temperature is lower, the
recovery is poor. If the temperature is any higher, the stibnite volatilizes
into oxide. This method is used to upgrade low-grade ores. The ore is placed on
a grate, and the stibnite melts out of the ore and through the grate to collect
melts at 550° C. (Pelabon); at 540° (Wagemann); at 546° (Borgstrom).
volatilizes, in the absence of air, between 650° and 917° (S.A. Chakhov and I.I.
Volatilization Roasting is the process of volatilizing the sulfur and forming
antimony crude oxide (Sb2O3)
+9O→Sb2O3+3 SO2; begins at 290°, rapid at 520°
and finishes at 560° (Saito); begins at 290°, if the size of the grain is 0·1
mm. in diameter, at 343° of 0·1 to 0·2 mm., and 430° if 0·2 mm. (Friedrich);
commences at 190°, proceeds energetically at 340° and terminates at 445°
(S.A. Chakhov and I.I. Slobodskai).
This is the process of de-sulfurizing sulfide ore where the oxide
is not volatilized but remains as the tetraoxide or pentoxide. The Sb2O4 and
Sb2O5 is then reduced t metal.
Sb2O3 + Sb2O5 --- Sb2O4
In this process, sulfur is removed from stibnite by using scrap iron in the
fusion. This also requires soda ash to enhance slag removal Sb2S3+3
FUMING CRUDE OXIDE TO
at above 445° (Chakhov and Slobodskai).
commences at 900° and finishes at 1030° (Chakhov and Slobodskai).
at between 750° and 800° (A. Simon and E. Thaler).
at 930° (A. Simon and E. Thaler).
REDUCTION OF CRUDE OXIDE
This is done using carbon and soda ash.
CO at red heat.
ELECTROWINNING OR OXIDATION:
3 Na2S = 2 Na3SbS3 Leaching
stibnite with sodium sulfide
+ 6NaOH = 2 Sb + 6 Na2S + 3 H20 + 3/2 02
+ 3 H = Sb + 3 NaSH Electrowinning
SULFIDE ORES: The
mineral dressing of sulfide ores is primarily accomplished by flotation although
it can be accomplished by gravity and hand -sort methods. Recoveries of
un-oxidized sulfides can be in the mid 90% range with concentrate grades of 60
to 68% for stibnite ores. The stibnite concentrates are then fumed to a crude
oxide that is either fumed to a finished oxide or
reduced to metal and then fumed to finished oxide. Tetrahedrite concentrates are
usually leached in alkaline solutions that are electro-won to recover antimony
metal or oxidized to sodium antimonite. Jamesonite concentrates are generally
reduced to antimony-lead bullion (generally 50%-50%) that is selectively fumed
to recover a crude oxide that is then reduced to metal and fumed to finished
Oxide ores are upgraded by gravity methods including jigs, tables, and heavy
media separators (HMS plants). The mineral dressing of oxide ores generally
result in recoveries of less than 50% and concentrate grades in the 25 to 40%
antimony range at best. These concentrates are typically reduced directly to
metal or fumed to crude oxide that is then fumed to finished oxide. In either
case, the cost of reduction or initial fuming requires massive amounts of fuel
and results in very high costs.
Stibnite ores are the most desirable due to high recoveries and lower costs of
conversion. Oxide ores are least desirable due to poor recoveries and the high
cost of conversion.